Time-limit circuit-breaker.



M. F. OWENS.

TIME LIMIT CIRCUIT BREAKER.

APPLICATION FILED NOV-23,1911- 1,144,233. Patented June 22, 1915.

3 SHEETS-SHEET I.

Qcci

z 2 Zoe M303 3331;; @aktozmeqs M. F. OWENS.

TIME LIMIT cmcun BREAKER.

APPLICATION FILED NOV. 23, I911- 1,144,233, Patented June 22, 1915.

3 SHEETS-SHEET 2- is 30 #54 '5 w w M. F. OWENS.

TIME LIMIT CIRCUIT BREAKER.

APPLICATION FILED NOV. 23, 1911.

1,144,233.. Patnted June 22, 1915.

3 SHEETSSHEET 3.

ll'l STATES P v MICHAEL E. OWENS, 0]! HARTFORD, CONNECTICUT, ,ASSIGNOKT0 AUTOMATIC REFRIGEBATING COMPANY, OF HARTFORD, CONNECTICUT,CORPORATION or JERSEY.

Specification of Letters Patent.

TIME-LIMIT CIROUIT- BREAKER.'

Patented June22, 1915.

7 Application filed November 2 3, 19,11. Serial 11o. 6 81,e7 9.

Hartford and Circuit-Breakers, of which the fol:

lowing is a full and clear specification, illus-v trated in theaccompanying drawings, the articular novel features of the inventioneing-more fully pointed out in the annexed claims.

My inventionrelates in general to circuit breakers which control thecurrent supplied toelectric motors, whereby the current is interruptedwhen it exceeds a predetermined amount, and in which besides by suitablemeans such excess .of current is permitted to flow to the motor during apredetermined time.

In particular my invention relates to cirouit breakers which permit anexcess amount of current to flow to themotor during its starting period,whereafter the sensitiveness of the device is varied so that the currentwill be interrupted whenever it should exceed a predetermined limit.

The accompanying drawings illustrate a wiring arrangement and thenecessary apparatus in diagrammatic form, since the detail constructionof the apparatus in particular may vary considerably according to therequirements in every given instance.

. In these drawings Figure 1 represents a diagrammatic arrangement ofcircuits in which a two phase alternating current motor is controlled,whereby the -main current is interrupted indirectly through the openingor closing of auxiliary circuits. Fig. 2

represents a diagrammatical illustration of similar character to thatshown in Fig. 1

applied to a motor supplied by three phase alternating current, and Fig.3 is a diagrammatical illustration of a two phase alternating currentsupply, whereby the main current is directly nterrupted :by the cutoutdevice.

In all three figures the wires which carry the main current su plied tothe motor are indicated by. heavy ines, whereas what are termedhereinafter the auxiliary circuits are indicated by light lines.

Referring to the modification shown in Fig. 1, a, b, c and d are ourmains or con F. OwnNs,

. lug 10 of ductors through which the two phase alternatlng current issupplied. 1 is the main switch which may be opened or closed by hand. isthe motor" to which the current s .supplledl The diagrams which I havellustrated ,in all three figures are in their arr ernent particularlyadapted to the control of an electric motor for driving refrigeratingmachinery, and therefore I have shown starting and stopping of the motoras effected hya. thermostat, which in all three figures 1s shown at 2.Moreover refrigeratsystems of the kind for which the system is intendedare also nowadays generally provided with what might be termed a highpressure cut out which responds to dangerously high pressure in therefrigerating system, and whereby the motor is stopped instantly as soonas this pressure has been attained. Systems of this kind are forinstancedescribed in a patent to Chamberlain and Marshall, No. 834,870,issued October 30th, 1906, and merely for the sake of completeness Ihave inserted diagrammatically a switch which interrupts the motorcurrent at such excessive pressure also in the present system, in orderto indicate where such high pressure cut out device may be located in mynovel cutoutdevice. In all three figures the high pressure cut offswitch is indicated at 3, and in all three instances it is assumed thatthis switch remains closed.

In Fig. 1 the cut out controller is shown at 4 and it consists of twosolenoids 5 and 6 each provided with a core 7 and 8 respecwhich cores indeenergized condition of the solenoids protrude at the lower ends oftheir coils and are arrested in this position by a stop 9 which may beintegral with zthe base plate, not shown, on which the whole device ismounted. The lower end of each core is provided with a lug 10, each ofwhich coiiperates with a bell crank 11. Each of these bell cranks hasone arm provided with a. latch 12 adapted 'to engage its adjacent core,arm 13 of each of the two bell cranks extends horizontally as clearlyshown. Moreover each bell crank, which is pivoted at 14 has a detent 15to which a spring 16 is attached in such manner that each bell crank,the' automatic control of the.

while the other tends to engage with its latch 12;the lug 1 4 weight 18from bell crankarms-13. The lower-endof rod 17 carries a piston 22 of adash pot 21 which operates in 'such'manextends vertical 17 arms/13:50that when it descends it strikes, these .arms and thereby removeslatches, 12

.from their. respective lugs, and to thusrendejr cores '7 and 8freetomove upward. Rod 17 also carries near its lower end core.- 19 of asolenoid-20 which is in such'pos i+ tion that when the solenoid isenergized its core 19 is drawnupward. and thus removes nerthat thepiston is freetomove. u ward but its downward movement is retar ed bythe action of the dash pot which'may be controlled through valve 23.Thus when sole- I noid 20 is energized and draws'in itscore 19, rod 17with weight 18 is free to fly-up tact.

ward, but when the solenoid deenergized core 19 with its weight 18 willgradually up'per'end of rod 17 carries a switch 24 which is closed whenthe rod 17 moves up ward,sand which is opened when thls rod starts onits downward movement. Moreover each core 7 and 8 of solenoids 5 and 6respectively carries on its upper end a rod" 25, each of which byitsupward movement opens a contact 26 by impinging upon a lever 27 pivotedat 28. The mam switch .30 which opens andcloses the circuit, di:

rectly leading to the motor may have any form known in the art which 'issuitable for control by a solenoid or the like. I have for instanceshown in this particular in- 4 stance a toggle jointswitch which has twoarms 31, 32, pivoted at 33 and 34 respectively. 'The arms coiiperatewith the contact elements 35 and 36 respectively. The switch is operatedby a rod 37 the lower end of which carries a solenoid core 38 whichprotrudes through the lower end of a solenoid 39 and'its upper end isconnected with an auxiliary switch 40 which may be of any suitableconstruction. Inthispar- 'ticular instance I have illustrated simply alever 42. pivoted at 41 and pivotally connected withrod 37 which carriesat its other end an insulated body/43 carrying two contact plates 44 and45 respectively, by which the auxiliary conductors shown adjacent tothese plates are connected with each other in the manner which will be.presently described. The thermostat 2 previously referred to has a startand a stop con- The connection between the several devices previouslydescribed-is as follows,

(main switch 1 being assumed as closed:) From conductor (2 the currentruns over switch 1, to'auxiliary conductor 50, to thermostat 2, which isassumed to stand on the start contact,-.thence ove'r conductor51, toplate-44, and over conductor 52 to solenoid 20 and the latter ductor50,switch 3 sink back underthe influence of the dash pot into its normalposition shown.- The main conductor a, without passing again throughswitch 1. This energizes solenoid countering the resistance of the dashpct 21. By this movement of 'rod 17 switch 24, dis} posed at its upperend, closes itslcontacts and simultaneously, by the removal of weight 18from arms 13 on which it normally rests as described, latches 12 arepermitted to lock solenoid cores 7 and 8 in the noids 5 and 6 beenergized by an excess amount of current which is conducted tothe motorin the manner to be describedfcores 7 and'8 can not be drawn into theircoils.

f'boil' 26,and "thence over conductor 55 to a has attached to it aweight18 in line" with byatti-acting its core 19 "throws up weight/18 withoutthereby 'en- Theclosing of contact 24 closes the following circuitrfromconductor at over con thence conductor 56 to contact 26 (normally,closed), thence over conductor '57 to the other contact '26 (alsonormally closed), thence over conductor 58 to solenoid 39, con- (assumedto be closed),

ductor 59, resistance 60, conductor 61, switch 24, conductor 62, back tomain conductor 0.- This circuit energizes solenoid 39 which therebyoperates the toggle joint of the auto matic motor switch 30, so that thelatter is closed thereby. By the upward movement causes itscontact plate44 to slide off conductors 51 and 52 and its contact plate 45 to connectconductors 63 and 64. This break between conductors 51 and 52 opens thecir-.

- of rod 37,when switch 30 is closed, auxiliary'switch 40 is thrown.upward which cuitthrough the thermostat 2and solenoid 20, so that thelatter drops its core 19, which, however, can only descend slowly onaccount ofthe retarding action of dash pot 21. On the other hand theconnection between conductor 63 and 64 through plate- 45 establishes apassage from solenoid'39 and resistance 60, over resistance 65,conductors 63, 64 and 66, back to main con-' ductor c in parallel. withthe connection over conductor 61, switch 24 and conductor t 62 to themain conductor c. This shunt passage over resistance 65. is maintainedas a shunt only for an instant, because at the moment solenoid 20.isdeenergized and its core commences to descend switch 24 is opened, sothat thereby the circuit over conductor'61, switch 24 and conductor 62to the main 0 is'interrupted. Thus notwithstanding the opening ofcontact 24, the oilcuit through solenoid 39, which controls v motorswitch 30, is not interrupted but the amount of current is only slightlylessened owing to resistance 65 being now interposed in this circuit.This will prevent undue heating of solenoid 39 by thecurrent which nowneed only be strong enough to hold core 38' attracted. The closing ofmotor switch .30 now connects mains a, l), and d with the motor throughthe following four lines main'a,' -switch 1, conductor 67; main b,switch 1, conductor 68, solenoid 6,-conductor 69, switch contact 36,over switch 30 and conductor 70 to the motor; from main. 0 over switchl,conductor 71 to the motor; from main (2 over switch 1, conductor 72,

to solenoid 5, conductor 73, contact 35, switch 30, over conductor 74 tothe motor.

' mediately after main switch 30 is closed solenoid 20 is de'e'nergizedso that weight 18 starts to descend, and also that during the raisedposition of weight 18 cores 7 and 8 are locked. Thus when the motorstarts upon closing of main switch 30, solenoids 5 and 6, whilesufficiently energized by the excessive starting current, are unable toattract their core, becausethey are locked by latches 12. The dash pot21 is set so that it will permit its piston and thus'weight 18 todescend within a predetermined time considered .suiiicient to acceleratethe motor to full speed so that its current will fall t6 normal.Therefore when after the lapse of this time weight 18 arrives at thebottom of its stroke and impinges upon arms 13, whereby latches 12 arewithdrawn from 'their respective armatures 7 and 8, these cores areunlocked and are now free to be drawn into thelr respective solenoids 5and 6, which latter, however, on account of the starting current in bothphases having now fallen to normal, are unable now to attract theircores. If on the other hand after such predetermined time through somecause the motor should not have attained its full speed or the currentshould still be of abnormal strength, whichshould call for an opening ofthe motor circuit, such abnormally strong current energizes solenoids 5and 6 sufiiciently to attract their cores. By the upward motion of coresand 8 their rod 25 impinges upon its lever 27 and the two contactsil6are opened thereby, so that the auxiliary circuit through solenoid 39which controls the motor switch 30 is opened.

- Through the dei nergizing of this solenoid 39 resulting therefrom;themotor switch 30 is opened and thus the main current cut 01?. Thisalso returns auxiliary switch 40 to its normal position shown. Theinterruption of the main current also deinergizes solenoids 5 and 6 sothat their cores 7 and 8 drop. Switches 26 are of such construction thatthey remain open even if cores 7 .and 8 drop back to their usualpositions, to

prevent automatic starting of the motor. This may be obtained forinstance by properly weighting the-uppercontact arms of these switches,so that they tumble inwardly when their 'lower arms are lifted by thecores 7 and .8, respectively. In order to enable the *device to startthe motor, these' switches must first be closed by hand,which thus callsthe operators attention tothe abnormal condition of the entire system.After these switches'are closed by hand all elementsare returned intotheir normal position and ready to start the motor up again if thethermostat remains on the starting contact." If during the normalrunning of the motor the condition of the refrigerating system shouldcall for the stopping of the motor, thermostat 2 in this case moves tothe stop contact. This closes a shunt circuit by the way of thermostat'2, conductors 7 6 and 59, resistances 60 and 65, over conductors T 63,64, 66 to main 0. Solenoid 39 is practically de'nergized thereby or atleast its current is reduced to such an amount that it is unable to hold.its core 38 and thus motor switch 30 is opened and the current cut offthe mot-or. Similarly to the manner previously described all the otherelements of the system return into their normal posi tion shown.

' It will be obvious to any one skilled in the art that the entirearrangement as previously described may be also applied to any otheralternating current system, for instance three phase alternatingcurrent. In Fig. 2 I haveshown how the starting ofa three phasealternating current may be controlled. In this figure all the elementscorresponding to those shown in Fig. 1 are provided with the samereference numerals. By comparing Figs. 1 and 2 it will be noted that thetwo arrangements difi'er only in the omission of mainconductor a of Fig.1 in Fig. 2. This main conductor a in Fig. 1 it will be noted runsdirectly over hand switch 1 to the motor.' To avoidrepetition I havetherefore omitted to further describe the arrangement in Fig. 2.

In Figs. 1 and 2 I have shown an arrangement in which, when an excessamount of current continues flowing through solenoids 5 and 6 beyond thepredetermined time set by the dash pot, the cores of these solenoids arereleased by weight 18 and are attracted and interrupt the auxiliarycurrent at switches '26, so that the auxiliary current through thesolenoid 39 of automatic motor switch 30 is interrupted and thus thelatter switch is opened. In Fig. 3 I have illustrated how instead ofinterrupting the circuit through solenoid 39 the main motor circuit maybe interrupted by switches 26 of cut out controller 4' in case ofcontinned excess. of amount of current-l The 'general'arrangement whichembodies this feature may be otherwise the same as the one shown in Fig."1, and similarly lto Fig. 1 I have shown this modification applied to atwo phase alternating current 'system. Likewise all conductors andelements which this modification has in common with Fig.1are denotedwith the same reference characters.- Fig. 3' difiers from Fig. 1 in-theomission. of the au'm'lia'ry connection 56, 57 and 58 leading fromswitch 3 to solenoid 39, in which connections the two switches 26 of thecut out control 4 are located in Fig. 1. Instead solenoid 39 is directlyconnected in Fig. 3 by conductor 80 with switch 3 and thence overconductor 50 with the main (2. The other end of sole- .noid. 89 isconnected with the system exactly in the same manner" shown anddescribed with reference to Fig. 1, so that a description thereof aswell as of the connection of solenoid 20 may be omitted from the de-,scripti'on. Now instead of connecting switches 26 of cut out controller4 in series with the auxiliarycircuit of solenoid 39 as just described,I connect these switches-in circuit with the main-conductors leading toautomatic switch 30. In Fig. 1, for instance, one main circuit leadsfrom main conductor (1 over switch 1, conductor 72, solenoid 5,conductor 73 to contact 35 of the automatic switch. Another circuitleads from main 6 over switch 1, conductor 68, solenoid 6, conductor 69to the other contact 36 of the automatic switch. I now placeswitches-26, which are opened when cores 7 and 8 of solenoids 5 and 6are attracted,

into these two main circuits in such manner that the circuit from main(1 leads over switch 1, conductor 72 to switch 26, thence from the othercontact element of this I switch over solenoid 5 and conductor 73 tocontact 35 of the automatic switch30, fromv where it runs the motor byway of conductor 74. The other circuit runs from main 6 over conductor68 to the other switch 26 and thence from this other contact elementover solenoid 6 and conductor 69 to contact element 36 of switch 30,whence it passes, over the switch and conductor to the motor M. If now,as described in detail with reference to Fig. 1, in the presentarrangement an excess amount of current should continue flowing into themotor after thepredetermined time has elapsed, cores 7'and 8 ofsolenoids 5 and 6are released by weight 18 and drawn into their coils,whereby, as also previously described, they open switches 26. Thus inthis case the two main circuits leading" to the motor from themain'conductors b and 01 respectively are interrupted which, however, inthis case, occurs without opening automatic switch 30. This calls the opv erators attention to the irregularity in the of the motor'circuitin-case of danger into a shown in Fig. 2, and the-chailges nry' in'Fig..-2" to convert the indirect-openmg direct openingof=it-are1similar to those ili lterigationsmade in= Fig.- 1 and shownin11g. Z-.- tni m 4-,

What'I claim is: 1 a time limit circuit breaker the com L bination withanelectricimotor, and main conductorssupplyingthe current thereto;

of a cut out controller and auxiliary-cirw cuits connecting. it withsaid main conductors, said controller having means responsive to anamount. of motor current exceed-' ing a predetermined limit forinterrupting the connectionbetween said mains and the motor, saidcontroller also having. means for automatically locking saidinterrupting -means during a predetermined time to permit the startingof the motor rupting the main circuit. 2. In a time limit circuitbreaker, the combination with an electric motor, and main conductorssupplyin the current thereto; of a cut out contro er and auxiliarycircuits connecting it with said main co'nductors, said controllerhaving solenoids lo- 16 cated in said main conductors and responsiveonlyto amounts of motor current in. excess of a predetermined limit, andcores located therein, causing the interruption of the motor circuitwhen their solenoids re spond, means tending to lock said cores ininoperative position, means tending normally to discharge said 'locln'ngmeans from their cores, a starting solenoid connected with saidauxiliary circuits for removing 71-10 said disengaging means from normalposition, to render said locking means operative when it is desired tostart the motor, means for closing the circuit through said solenoid,and means for denergizing said starting 1 5 solenoid to permit return ofsaid disengaging means to normal position, a dash pot for controllingthe return of said means to its normal position within a predeterminedtime, thesolenoid cores of said controller 120 causing the interruptingof the motor current after said predetermined time an excess amount ofcurrent continues passing throu h said solenoids.

without intera atime limit circuit breaker, the 'com- 12:

. masses cuitqo nsc ngit with ai m n! endear, saidoontr l r havlng. ol nd loca ed i said; conduct rs and r spo si e. on y.

' to. amounts of, motor current in, excess of. a

predetermined limit, and cores located'there -i n. cau ingthe in e mr ino t e t um n. when, heir s n ds re pon mea s tending't loc said cor sininoperativo poitin,jme -nsn mnai11y tending to diseng ge.

saidlock na fromt eir cores, 4 art.- ing solenoid connected withsaidauxiliary circui s. for m v g. sa d I dis ng gin malls iromnoxmalposition to render sai 1QCkil g;mQ3 operative when it. is desired to.start the motor, means for closing the rcuit m ugh said solenoid, andsolenoid connected with said, auxiliary circuits for los ng; said.motor, switch, a, witch 11..-

- of said nected with'said diseuga ing m a s or 01 s.- ing saidmotor-switch sgienoid circuit when al. means. are rem ved. from. ormposition; an auxiliary switch. for opening a d,

starting-solenoid circuit and for closing a,-

shunt-to... the switch operated by said disenagi g: means when he motorSwi c i c osed ,.a daSl.1-,PQt for controlling the return disengagingmeansrto n rmal po ion. within a predetermined time, the soleole oidsnoid. coresoi said cut-out; controller causing the i'nterruptingof themotor current idi-predetermined timeifian excess amount of cur nt cntinues passing through their 4,. In a time cir ui reaker, the. c m:bination with an electric motor, main Condu ors supplying the currentthereto ands solenoid. operated motor switch. in. said mam conductorsforgcontrolling the current sup-.

ply to the motor; of a-cut out controller and auxiliary circui s. c necin"; it with said main conductorss'aid controfier having sole-.noidslocated insaid main condu t r n responsive only. to} amounts. of.motor. ourrent in excess ot a predetermined limit, andcoreslocatedtllerein, means tending to. lock said cores in inoperativeposition, a, weight :Eor; normally holding said locking mea s ininoperative position, a starting solenoid 0 .11.-

nected' with said auxiliary circuits for lifting said weight to rendersaid locking means operative when it is desired to start the motor,means for closing the. circuit through said solenoid, and a solenoidconnected with said auxiliary circuits for closing said motor switch, aswitch connected with said weight for closing said motor switch solenoidcircuit when in lifted position, an auxiliary switch for denergizing theweight-solenoid and for closing a shunt to said weight switch when themotor switch is closed, a dash pot for controlling the droppin of saidweight to its normal position wit in a predetermined time, thesolenoidcores of saidcut out controller interrupting the auxiliary circuitthrough said motor switch solenoid aiter such predetermined time if anexcess ainount'of current continues passing through h i o en 5 In a timelimit circuit breaker, a cut out controller having two main 1 solenoidseach connected in series with the main circu1 t to be-broken, and acorefor each sole: noid', a latch for each core normally tending to lockitscore in detinergized position, a bar disposed substantiallyvertically between the,

twosolenoids having a wei ht attached to, it

resting. upon both of' sai latches to normally, unlock said cores, astartin solenoid? having its core connected with said bar, and a dashpot also connectedwith said bar per-- mittingfree upward movement ofsaid bar and said weight when said core is drawn in. by its solenoid,but causing said weight, to drop within a predetermined time when saidstarting solenoid is d'e'einergized, a switch adjacent to each core ofsaid main solenoids 6. in a tune limitcircuit breaker, thecom b1nat1on'with an electric motor, and main conductors supplying the currentthereto; of a cut out controller, auxiliary circuits connecting it withsaid'main conductors, said controller having means responsive to anamount oi motor current exceeding a predetermined, limit forinterruptingthe connection between said means. and the motor, said,controller also.having automatically operating means for-rendering saidinterruptingmeans inoperative during a predetermined. time to. permitthe starting of the motor without interrupting the main circuit.

7 In combination, an. electro-responsive switch, anelectro-rcsponsiverelay associated therewith. and deenergized upon operation thereof andan overload tripping device for said switch, said relay when energizedrendering said device inefi'ective and having means for retarding itsoperation when deenergized to maintain said switch independent of saiddevice for a definite period after operation of the former.

8 In a motor controller, in combination,

electro-responsive starting means, overload tripping means and anelectro-responsrverelay responsive to energlze said starting means andto render said overload means inefiective, said relay being deenergizedupon response oisaid starting means and having means for retarding itsreturn movenient to mag.tutam a 'ness of said tripping means.

9,. In combinat1on,a protective device for electric circuits,'electromagnetic means con-r '"trollingthe'continuity of the circuit tobe means interlocked 'with said oi'meielectromagnetic means-to render"said protective device ineffective for a temporary periodafter closureof the circuit to be pro- ;QLOQThe combination with an automaticprotective device comprisinfi'a switch controlling the continuity odevice therefonand electro-responsive means responsive prior to closureof said switch to; render, said tripping means inefiective deenergizedupon closure of said switch to render said tripping means eifectiveafter a'tempora'ry period."

11. The combination with an automatic pr'otectiveidevice, incl .a switchcontrolling the continuity of t e circuit to be.

' protectedandan electromagnetic tripping load tripp' responsiveeviceresponsive to -mechani- 40 1 device therefor, anelectro-responsivedevice responsive to render said tripping deviceinefiective and having means for retardingjts movement when deener saidelectro-l, onsive device and sad swltch being in-.

' ter ocked to necessitate energization of the' former prior to, closureof the latter and to ileiinergize the former upon closure ofthe atter.'.i

12. The combination an automatic.-

protective device including -an electro-responsive switch controllingthe continuity of the, circuit to be protected and overdeviee thereforof an electrocally lock said overload deviceagainst operation and havingmeans for retarding its I operable to mechanically lock said deviceoperation .to release said overload I device, and electrical interlocksbetween said electro-responsive device and saidelectro-responsive switchnecessitating energization of the former prior-to ener tion ofthe latterand effecting deenergizationof the former upon response of the latter.

13. In combination, anautomafic protec-I tive device for electriccircuits and means against operation, said means v f t e" circuit toprotectedand an electromagnetic tripping "'Witnesses':

automatically operate tosaid means for retarding" the automatic.

and movement of said former means to maintain said device locked for a'periodof .14.-In combination, a protectivadevice for electric clrcuitsand. means for mechani-' cally locking said device prior to closure ofthe-circuit to be protected and automatik 'cally releasing said deviceafter the lapse of a predetermined period of time.

15. In combination, an automatic protective device :for electriccircuits, electromsponsive means for mechanically l ki said deviceagainst operation prior to closure of the circuit to be protected, meansfor device against operation prior to closure of said circuit andautomatically releasing said deviceupon the lapse of a period 10f, time.

tive deviee for electriccircuits, el

W .net1c means -controllmg the continuity of mbination, automatic thecircuit to be protected, and electromag, netie means interlocked withsaid former means to render said protective device in? efiective priorto closure of the circuit to be controlled and to subsequently'renderprotective; device efiective.

18. In combinat on,

I 'utoma'tic protective-device for electric means controlling the,continuity of the circuit to be protected? and means interlocked withsaid former means to render said protective device .inefiective uponclosure of the circuit to becontrolled and .to automatically render Isaid protective device 'efiective after" the lapse ofa definite eriod'oftiirner 1F- W "J. K; Hunnrox, Ji-.,

